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chris del
02-23-2007, 10:23 AM
For those of you that have been faced with having to replace your lathe motor who decided to go with a AC motor and VFD, or DC motor and DC drive?

In either case have any of you had problems in your variable speed drives caused by dust?

TYLER WOOD
02-23-2007, 10:46 AM
AC will be a lot cheaper I think. But if money was no object???

Paul Engle
02-23-2007, 10:51 AM
Tyler, by all means go with DC and electronic speed control 2 hp new would run 5 to 7 hundred $ see the Craft supplies cat they have one for 565$ i think. or go to the Baldor web site they have tons.. Just imagine turning an out of balance blank at 10 rpm....with full torque... ooooo baby sweet !!!!!!.

John Hart
02-23-2007, 10:56 AM
My lathe has a DC motor with an integrated Variable Speed Controller mounted into the headstock. There are vents on the headstock that do allow dust to accumulate on the circuit board and the board itself has a cooling fan mounted on it. I am somewhat negligent in cleaning the circuit board compartment, but do it every few weeks when I think about it. To date, I've had no problems with the circuit....other than a burn-out that I caused due to stupidity early in my turning endeavor. Another aspect to the DC motor is the brushes. I've replaced them once. Can't say for sure how many hours on the original brushes....but it's been probably 400 or so projects. They were $20 a set.

chris del
02-23-2007, 11:33 AM
AC will be a lot cheaper I think. But if money was no object???

AC is not cheaper. Yes AC motors are less than DC motors. But the AC VFD's are allot more than the DC drives.

Charles McKinley
02-23-2007, 12:12 PM
Hi Chris

Do you have a friend that is an industrial electrician or electrical engineer? If you do ask them if they can help you find parts on ebay or an industrial recycler in your area.

A used 3 phase electric motor should be about $10 per horse power and VFDs are availabe but you need to understand what you are buying and hooking it up.

If you can find someone to help you you could take them to a very nice dinner or the equalivant thank you and still be $$$ ahead.

chris del
02-23-2007, 1:28 PM
Hi Chris

Do you have a friend that is an industrial electrician or electrical engineer? If you do ask them if they can help you find parts on ebay or an industrial recycler in your area.

A used 3 phase electric motor should be about $10 per horse power and VFDs are availabe but you need to understand what you are buying and hooking it up.

If you can find someone to help you you could take them to a very nice dinner or the equalivant thank you and still be $$$ ahead.

Charles

I have great access to components and I am somewhat knowledgable as to the uses in industry, but was more or less fishing around for what tends to be the most common in Lathes specifically.
What ever I decide to use (AC or DC) I will be getting a NEMA 4 (washdown) control, that is water and more importantly sawdust tight!

Rich Souchek
02-23-2007, 2:18 PM
New AC motor and new VFD in the 1.5 hp range cost me less than $225 when I repowered my ol' Delta 12" lathe last summer.
The motor is a new Marathon 1.5 hp 1175rpm 220v/480 volt 3 phase without a base for $30 off Ebay. I built a wooden craddle and keep it there with strap pipe clamps.
The VFD cost me $160 new out of Atlanta from Automation Direct (I believe.) It is rated for an Ac motor of 1.5 hp with a 220 volt single phase input.
I thought it would be difficult to install and set-up, but it turned out simple.
Mount motor and setup v-belt drive to lathe. I added a 2 step pully on the motor to give me additional torque down now for bowls. The larger pulley gets the top lathe speed up to 2400rpm or so.
Regular 4 wire cable from motor to VFD, strip wire, screw the leads in.
Screw power in leads from breaker box.
Program the VFD with about 12 parameters, mostly giving it motor details and the stop/start ramps.
Then stand back and hit start.:)
VVVVVVVVVVVVVVVVVVVRRRROOOOOOOOOOOMMMMMMMM:D
She's going.
I have messed up christmass light before, but this installation was pretty much a now brainer.:p
The motor runs good, I loved the flexiblilty added by the VFD. Ramping to a stop in 5 seconds is nice. Reverse helps tremendously with sanding and finishing. Bowls can start off at 60 rpm, and then get finished at 800 rpm.
The DC drives were confusing to me, I couldn't figure out exactly what was needed and it seemed to cost much more when I bought anything new.
I ran the 12" AC drive Delta lathe for about 5 months trouble free before getting a PM 3520B for bigger bowls and their VFD AC motor.
(My old lathe is for sale now also. If interested, send me a PM.)
Rich S.

Bill Boehme
02-23-2007, 3:30 PM
Charles

I have great access to components and I am somewhat knowledgeable as to the uses in industry, but was more or less fishing around for what tends to be the most common in Lathes specifically.
What ever I decide to use (AC or DC) I will be getting a NEMA 4 (washdown) control, that is water and more importantly sawdust tight!
Chris,

If you can get a TEBC motor, it won't run quite as hot as a TENV washdown motor.

A few other miscellaneous comments:
There is no perfect system. Both AC and DC motors and drives have their strong points and disadvantages. Cost is one of the main factors.
Whatever motor you use, make certain that it is rated for variable speed duty over the range that you want.
Motors run a LOT HOTTER at slow speed so make sure that the temperature rating is adequate.
If you can get some expert help, it would be to your advantage. Even though programming the controller can be deciphered if you have a good manual, the mechanical part of the drive is up to your own expertise. Two important factors in the design of the pulley ratio are reflected moment of inertia and low speed torque at the load. Without proper design, you may encounter what is known as "hunting" with large turnings at low RPM where the speed is not able to stabilize, but instead swings back and forth over a range -- another term to describe this would be surging.
If your previous system used a fixed speed motor and a pair of cone pulleys (in other words, the stepped sheaves), it is very likely that your new variable speed drive will require a motor rated at least twice the horsepower and a two-step pulley arrangement. If your new motor is less than twice the HP of the old one then you may want to consider a three-step pulley pair OR stick with the pair of cone pulleys that you had before.
Your variable-speed system will have the best performance when the motor is running near its base speed for most of your turning. Choosing the right pulley ratios can help to optimize this situation.
If you can build your drive using J-section belts and sheaves, they will give the highest effficiency (around 97%). Their operation will also be very smooth and quiet.
Pulley diameter is also important. For J-section belts, the maximum belt speed is around 6000 feet per minute. That is also the maximum rim speed for most J-section pulleys. The other limitation is minimum pulley diamter because this affects belt wrap radius.
AC motors and VFD's are a bit better than DC motors and drives because the AC system is able to deliver full torque over the range of minimum speed up to the motor's base speed ("base" speed is the speed that the motor runs at when operated at 60 Hz which is around 1750 RPM for four-pole motors). On DC motors, the maximum torque is inversely proportional to speed. Also, above base speed, the AC motor is able to provide maximum HP up to its top speed whereas the DC motor becomes less efficient.Bill

M Toupin
02-23-2007, 7:48 PM
Bill provided some very good info, check out this thread for a bit more in depth discussion http://sawmillcreek.org/showthread.php?t=39536.

In the last few years the prices on new VFDs has plummeted and used 3ph motors are plentiful. A rough average for used 3ph motors is about $10 per hp. A 2hp setup with a NEW VFD and a used 3ph motor can be had for around $200. With some hunting and fleebaying you could get off a lot cheaper than that.

Mike

Jason Anders
02-24-2007, 11:29 PM
There are some pretty decent prices on variable motor packages. from www dealerselectric com site. I was referred recently to this site while searching for Lathe Motor swaps. I've bookmarked it for the future :D Kenneth over at theturnersshop swapped one in on a Nova 3000 lathe from there.

Bill Boehme
02-25-2007, 1:21 AM
There are some pretty decent prices on variable motor packages. from www dealerselectric com site. I was referred recently to this site while searching for Lathe Motor swaps. I've bookmarked it for the future :D Kenneth over at theturnersshop swapped one in on a Nova 3000 lathe from there.
It looks like they do have a wide selection of equipment. I did not check their rating. If you don't mind waiting for the right deal and are willing to spend the time perusing the AC Drives section on eBay, you can come up with much better deals occasionally. A couple years ago, the drives and motors sold for almost nothing because that is a part of eBay that had very little visibility, but things have changed and prices continue to rise dramatically as a result.

Bill